iTerm.sh improvements

Not sure if these commits are worth merging back, but I'd got two issues with iTerm.sh which I fixed for myself:
* iTerm.sh was launching two instances of terminal on first use (in osx 10.8, at least)
* Desktop was being switched from the current one, if there was a terminal instance on another desktop.

There is another file being changed, Terminal.py, which I adapted to run in SublimeText3 beta. It should certainly not be pulled, since it will break the plugin for ST2 users, but I don't know how to remove it from pull request, unfortunately.